Q. A 31-year-old female presents to the emergency department complaining of severe lower abdominal pain for the past two days. She reports a history of dysmenorrhea but stated that the current pain is much worse than her usual menstrual cramps. She denies any recent vaginal bleeding, fever, or urinary symptoms. She is not pregnant and has no significant medical or surgical history. On physical examination, she appears uncomfortable and is clutching her lower abdomen. Her vital signs are stable, and her abdominal examination reveals tenderness in the lower quadrants. You perform a pelvic examination, and the cervix appears normal. There is no adnexal tenderness or masses. Given the severity of the pain and the absence of any other apparent cause, the patient is admitted to the hospital and undergoes a hysteroscopy. Significant scar tissue is found in her uterus, which is causing obstruction of the uterine cavity (see image). The scar tissue is removed, and a biopsy is taken. The results of the biopsy are negative for malignancy. Following the procedure, the patient is started on a course of antibiotics and analgesics and is observed overnight. Which of the following is the most likely underlying cause of this patient’s diagnosis?